1. Field of the Invention
The present invention relates to an electromagnetically actuating optical deflecting element suitable for small devices, particularly relates to physically improved beams which support a movable component of the optical deflecting element.
2. Brief Description of the Related Art
Various types of small-sized optical deflecting elements produced by MEMS (Micro Electro Mechanical Systems) processing technology have been proposed, produced their prototypes and practically employed in optical deflecting systems in order to downsize optical deflecting systems or to produce them at lower costs. Various types of the optical deflecting elements which are actuated by electrostatic method, electromagnetic method, other method or the like, are proposed. For example, various types of the optical deflecting elements actuated by principle of galvanometer (a movable coil actuated by electromagnetic force) are proposed (so that the deflecting elements also are called “galvano mirror”) and manufactured by the MEMS processing technology based on the semiconductor manufacturing technology.
These optical deflecting elements employ, for example, beams constituted by a composite beam structure formed out of single crystal silicon and metallic wires on the crystal as shown in FIG. 16 (see references 1 to 3). Because the MEMS processing technology based on the semiconductor manufacturing technology is excellent in processing silicon and aluminum thin film with high precision, and a beam structure which determines actuating performance of the optical deflecting element can be formed with high precision without difficulties. Further since silicon is an elastic material, it is suitable material for the beam structure of the optical deflecting element. Optical deflecting elements based on the silicon are designed and manufactured so as to have actuating frequencies from ca. 200 Hz to several kHz, and employed in various measuring instruments.
Recently, optical deflecting elements actuated at low frequencies less than 150 Hz and in wide deflecting angles more than 50° have been required for applying to, for example, bar-code readers and the like. However, various technical problems arise in realizing such optical deflecting elements by utilizing only the composite beam structure consisting of single crystal silicon and the metal wiring. Hereinafter these problems are explained as referring to FIGS. 17 and 18.
FIGS. 17 and 18 are plan views of optical deflecting elements employing the beams made of single crystal silicon actuating at low frequencies, and these views are for explaining how difficult to constitute downsized optical deflecting elements. In order to actuate the optical deflecting element at a frequency less than 120 Hz, it is necessary to design a long, fine and thin beam, because single crystal silicon has a large Young's modulus of ca. 130 GPa. For example, since the single crystal silicon has a large Young's modulus of ca. 130 GPa, when a movable component is a square of side 3 mm, an optical deflecting element which can actuate at a low frequency less than 150 Hz can be realized by employing a beam with a length more than 20 mm, width less than 30 micrometer and a thickness less than 5 micrometer.
However, as shown in FIG. 17, a beam 508 is formed as a longer one, so that it is restricted to downsize an optical deflecting element 516 up to a certain extent. In order to downsize the optical deflecting element, a folded structured beam 608 might be possible as shown in FIG. 18. However, since silicon is a brittle material, the long, finely and thinly formed beam 608 is apt to be broken and there is a problem in its productivity. Even if such problematic beam is successfully produced, the beam 608 apt to be broken when it is dropped, so that such beam can not be employed by portable products and the like which require sufficient impact resistance, which means applicable fields of such beam are limited. The aluminum wiring is usually employed as the metal wiring to supply power to a coil wiring 612. However, since aluminum has a large Young's modulus of ca. 70 GPa, the beam must be formed much longer, finer and thinner taking influences of the aluminum wiring into consideration.
As explained above, practically it is impossible to produce a downsized optical deflecting element capable of being actuated at low frequencies from the composite beam structure constituted by single crystal silicon and the metal wiring.
As methods to realized optical deflecting element capable of being actuated at low frequencies, methods for utilizing composite beam structures constituted by combinations of polyimide resin and the metal wiring have been proposed (see references 4 to 7) as shown in FIG. 19.
Since polyimide resin has a lower Young's modulus from ca. 2 GPa to ca. 10 GPa than that of single crystal silicon and since polyimide resin is a soft material, a further downsized optical deflecting element can be realized by utilizing a beam 708 constituted by a combination of a polyimide plate 717, a polyimide plate 718 and a metal wiring 719 than by the combination of single crystal silicon and the metal wiring.
For example, when a movable component is formed as a square of side 3 mm, an optical defecting element capable of being actuated at frequencies less than 150 Hz can be realized by setting a length of the beam 708 more than 3 mm, a width of the beam 708 less than 30 micrometer and a thickness of the beam less than 30 micrometer. In addition, since polyimide resin is not so brittle as single crystal silicon, it can be expected to produce an optical deflecting element with higher impact resistance. Since the semiconductor processing technology can be applied to a polyimide processing technology, it is expected to manufacture optical deflecting elements with high precision.
Usually the aluminum wiring is employed as a metal wiring 719 for supplying power to an actuating coil 712. However, since aluminum has a large Young's modulus of ca. 70 GPa, the beam 708 should be formed much longer, finer and thinner taking influences of the aluminum wiring into consideration. For example, when the beam 708 is constituted by a combination of the aluminum wiring having a thickness of 5 micrometer by a width of 6 micrometer and polyimide resin, a length of the beam 708 should be more than 20 mm in order to actuate at frequencies lower than 150 Hz, so that possibility to downsize the optical deflecting element is restricted to a large extent. Also the impact resistance of the beam is reduced, because the beam is finely, long and thinly structured. Since the metal wiring such as the aluminum wiring does not behave as an ideal elastic body when the optical deflecting element is actuated in a wide range, but plastically deformed. As a result, since such metal wiring affects elastic deformation properties of the beam of the optical deflecting element, the metal wiring is not a suitable material for the beam of the optical deflecting element.
As explained above, practically it is impossible to produce a downsized optical deflecting element capable of being actuated at low frequencies from a composite beam structure constituted by polyimide resin and the metal wiring.
As a way to realize an optical deflecting element capable of being actuated at low frequencies, an optical deflecting element 816 manufactured based on a flexible substrate manufacturing technology as shown in FIG. 20 is proposed. The optical deflecting element 816 manufactured in the following manner is proposed (see reference 8). A polyimide sheet component 803 having a beam structure is formed. A reflecting plate, which is formed from a silicon substrate by the semiconductor manufacturing technology, is stuck on to the polyimide sheet component 803. A metal wiring 817 used as a looped jumper wire for supplying power to a plane coil 812 connects two electrode terminals formed outside a beam 808. This technology can be applied to the beam 808 which is mainly formed out of polyimide resin employed as a material having a low Young's modulus. The metal wiring 817 used as the jumper wire reduces a mechanical burden on to the beam 808. In addition, the looped shape of the metal wire 817 can suppress the metal wire from plastic deformation. Therefore, this technology is promising in order to realize an optical deflecting element capable of being actuated at low frequencies.
However, when a jumper wire with a diameter 20 micrometer or more is employed as the metal wiring 817, the metal wiring 817 gives a mechanical burden on the beam 808 to some extent, so that resonance frequencies of the respective optical deflecting elements vary due to dimensional dispersions among the manufactured beams. Consequently, since the resonance frequency is sensitive to product quality of the beam, it is difficult to manufacture optical deflecting elements at a low cost. The optical deflecting element can not be downsized due to the looped (jumping) metal wiring 817. Further, land areas 818 used as the electrode terminals for wiring the metal wiring 817 must be arranged on different positions from the reflecting plate, which hinders the optical deflecting element from downsizing. Since the polyimide sheet component 803 is soft, it is difficult to form the metal wiring 817 used as the jumper wire on the polyimide sheet component 803 by utilizing wire bonding technology, and there is a possibility that the polyimide sheet component is broken when wired. Further it is difficult to fix the jumping metal wiring 817 on to the unstable polyimide sheet component 803 used as the movable component in a stable state.                Reference 1: Japanese laid open Patent No. 2000-35549        Reference 2: Japanese laid open Patent No. 2004-198648        Reference 3: Japanese laid open Patent No. 2005-195639        Reference 4: Japanese laid open Patent No. 10-123449        Reference 5: Japanese laid open Patent No. 11-202254        Reference 6: Japanese laid open Patent No. 11-242180        Reference 7: Japanese laid open Patent No. 11-305162        Reference 8: Japanese laid open Patent No. 2005-99063        